The present invention relates generally to control of an implement operably coupled to a body of a vehicle, and more particularly to the estimation of the attitude and position of the implement relative to the body of the vehicle.
In various grading applications with a dozer, it is necessary to control the position and attitude of the dozer blade. Accurate measurements of the position and attitude of the dozer blade are required for accurate control. Most of the control systems available on the market today use direct measurements of these parameters. The position of the dozer blade can be measured, for example, with a Global Navigation Satellite System (GNSS) receiver or a laser system. In these systems, a mast is installed on the dozer blade to support a GNSS antenna, a laser prism, or a laser receiver. The attitude of the dozer blade can be measured, for example, with two GNSS antennas, two laser prisms, or two laser receivers. Each GNSS antenna, laser prism, or laser receiver is supported by an individual mast installed on the dozer blade. Other sensors, such as a fluid slope sensor, can be used to measure the attitude of the dozer blade.
Other sensors can be mounted on the dozer blade. A magnetic sensor, for example, can be used to estimate yaw. A magnetic sensor, however, is very sensitive to the local magnetic anomalies induced by the dozer itself and by magnetic objects (such as iron objects) near the dozer. Calibration of the magnetic sensor can remove the influence of the dozer but not the influence of magnetic objects near the dozer. The accuracy of yaw estimation with a magnetic sensor, consequently, is typically not better than few arc degrees, even when a gyro is used for filtering magnetic sensor measurements. A magnetic sensor, therefore, is typically used only for a vehicle that moves on a surface with a slope less than a predetermined maximum value (which is dependent on the required grading accuracy for a particular application) and for applications in which a yaw error of a few degrees is acceptable.
Many of the above-mentioned sensors, when mounted on the dozer blade, however, are not robustly protected from harsh environmental conditions, including shock, vibration, and impact with soil, stones, and rocks. Sensors mounted on a mast, in particular, are exposed and susceptible to damage. For a GNSS antenna mounted on the dozer blade, furthermore, the coax cable running from the GNSS antenna to the navigation receiver, typically located in the dozer cabin, is susceptible to damage.
To eliminate reliability issues associated with sensors mounted on the dozer blade, some measurement systems use only sensors mounted on the dozer body, preferably within the interior of the mainframe, inside the cabin, or on the roof of the cabin. The optimal location for mounting position sensors, such as a GNSS antenna, a laser prism, or a laser receiver, is on the roof of the cabin. To calculate the position of the dozer blade from the measured position of the cabin, the attitude of the dozer body relative to the ground and the position of the dozer blade relative to the dozer body need to be estimated. The attitude of the dozer body can be estimated by various combinations of inertial measurement units, GNSS antennas, laser prisms, and laser receivers.
European Patent Application Publication No. EP 2 187 166 discloses using video cameras mounted on the dozer body to estimate the dozer blade position relative to the dozer body by tracking special passive or active targets mounted on the dozer blade. The video cameras, however, require a stable mechanical environment for proper operation. The camera system is also sensitive to lighting conditions and fog, dust, and dirt in the optical path between the cameras and the targets. Infrared cameras can be used to overcome issues arising from light sensitivity; however, fog, dust, and dirt remain problematic.
In another approach for determining the attitude and position of the dozer blade, the kinematic structure of the dozer is modelled as a system of lever arms, pivots, and extended cylinders. In this model, the position of the dozer blade relative to the dozer body can be calculated if all lever arms (distance between pivot points) of the blade suspension is known. Lever arms of constant length can be easily measured directly or read out from mechanical drawings.
To measure cylinder extension, a linear displacement sensor based on a potentiometric sensor or a magnetorestrictive sensor can be used. A linear displacement sensor mounted on the outside of a cylinder, however, typically does not operate reliably and can be easy damaged by soil, stones, or rocks. Placement of a linear displacement sensor inside a cylinder overcomes reliability issues. Standard commercial cylinders for construction machines, however, are not outfitted with internal linear displacement cylinders; and retrofitting existing construction machines with custom cylinders is an expensive and time-consuming operation.
A robust method for determining the attitude and position of a dozer blade, or other implement, in which sensors can operate reliably under harsh environmental conditions, is desirable.